The source for the
comes with two
documents by Eric Allman that are required reading.
Sendmail - An Internetwork Mail Router
, including its underlying theory.
Sendmail Installation and Operations Guide
installation instructions and a succinct description of the configuration
Many vendors also provide online manuals
which may reveal vendor-specific customizations
not documented in this book.
Also, if you have the source, see the files
A complete understanding of
is not possible without at least
some exposure to Request for Comments (RFC)
issued by the Internet Engineering Task
Force (IETF) at the Network Information Center (NIC).
These numbered documents define (among other things) the protocols
and operational requirements of the Internet.
RFCs are available via anonymous FTP. See the
Bibliography for information about how to retrieve individual RFCs.
transports mail from one machine to another
over a TCP/IP network, it does so using a protocol called the
Simple Mail Transfer Protocol
, or SMTP for short.
SMTP is documented in RFC821.
The division of mail messages into a header and a body, as well as
the syntax and order of header lines are all defined in RFC822,
Standard for the Format of ARPA Internet Text Messages
It also describes the syntax of addresses.
RFC819 is entitled
Domain Naming Convention for Internet User Applications
and describes the hierarchical form of host naming used today.
This document defines the form a hostname must take.
RFC976 is entitled
UUCP Mail Interchange Format Standard
the format of mail messages transported between machines using UUCP.
RFC1123 is an extension to RFC821 and RFC822. It makes several
amendments to the original documents and cleans up some previously
RFC1521 and RFC1522
RFC1521 introduces and describes the standards for Multipurpose Internet
Mail Extensions (MIME).
MIME provides ways to embed non-text data (such as images, sounds, and movies) inside
ordinary email messages.
RFC1651, RFC1652, and RFC1653
RFC1651 describes a general extension mechanism for SMTP, called ESMTP.
RFC1652 describes an extension for transport of 8-bit data, called the
8BITMIME extension. RFC1653 describes an extension for message size
Section 34.8.22, EightBitMode (8)
RFC1891, RFC1892, RFC1893, and RFC1894
SMTP Service Extension for Delivery Status Notifications
(DSN), describes the ESMTP RCPT command's NOTIFY, RET,
and ORCPT extensions. It also describes the ESMTP MAIL
command's ENVID extension.
The Multipart/Report Content Type for the Reporting of
Mail System Administrative Messages
, describes the
header requirements for DSN. It also describes the order and
MIME parts of a mail status
report's mail message.
Enhanced Mail System Status Codes
describes the meaning of the DSN status number
An Extensible Message Format for Delivery Status Notifications
describes the machine readable part's header-style keywords, for the
machine readable part of the DSN return message described in RFC1892.
Two topics that are only touched upon in this book are
The Domain Name System (DNS) and
TCP/IP network communications. At a typical site, a significant number
of problems with mail turn out to be problems with
one of these other areas, rather than with
The Domain Name System is well documented in
DNS and BIND, Second Edition
Albitz and Cricket Liu (O'Reilly & Associates, Inc., 1997).
The protocols used to communicate over the
Internet are well documented in the book
TCP/IP Network Administration
Craig Hunt (O'Reilly & Associates, Inc., 1992).
Finally, many mail problems can only be solved by the system
program runs as
and can only be installed and managed by
The art of functioning effectively as
is superbly covered in
UNIX System Administration Handbook
by Evi Nemeth, Garth
Snyder, Scott Seebass, and Trent R. Hein (Prentice Hall, 2nd edition 1995).